The invention relates to an apparatus for driving rod for rotation in which a rod is driven to rotate through a given angular extent and its rotation is stopped at a given angle or angles of rotation, and in particular, although not limited thereto, to a rod actuator which drives an oil pressure controlling rod used in a shock absorber of a vehicle suspension to a given angle of rotation
In one form, a shock absorber of a vehicle suspension generally comprises a cylinder containing a quantity of oil and a piston which divides the internal volume of the cylinder into two parts. The cylinder is connected to an axle while the piston is connected to a car body through a hollow piston rod. As mentioned, the piston divides the internal volume of the cylinder into two portions which communicate with each other through a channel. An oil pressure controlling rod extends through the piston rod into the channel. A rotary valve which regulates the flow area of the channel is incorporated into the piston, and the rod is secured to the rotary valve. When the rod is rotated in one direction, the rotary valve rotates in the same direction to increase the flow area of the channel to reduce the resistance presented to a flow of oil from one to the other of the divided portions within the cylinder or a flow in the opposite direction, thus facilitating a movement of the piston. In other words, the vertical oscillation of the piston and hence of the car body is reduced as compared with the vertical oscillation of the cylinder or the axle, increasing the load applied to a suspension spring while reducing the attenuation exerted by the shock absorber. Conversely, when the controlling rod is rotated in the opposite direction, the flow area of the channel is reduced, providing an added resistance to the movement of the piston. In other words, the vertical oscillation of the piston increases as compared with the vertical oscillation of the cylinder, decreasing the load applied to the suspension spring and causing the shock absorber to exhibit an increased magnitude of attenuation.
An actuator is coupled to the controlling rod in order to establish a given angle of rotation of the controlling rod or the flow area of the channel. Such actuator comprises an electric motor, a reduction gearing which provides a speed reduction to the rotation of the motor before it is transmitted to the controlling rod, and a plurality of switches or a potentiometer which detects an angle of rotation of the controlling rod. A shock absorber control system includes means for providing a command which establishes the attenuation to be exerted by the shock absorber or an angle of rotation of the controlling rod, and a motor control circuit which compares the command against a signal from the switches or the potentiometer to drive the controlling rod to a desired angle of rotation.
In another form, the shock absorber is additionally provided with an air chamber which is subject to pressures produced by an oscillation of the axle, and an auxiliary air chamber which communicates with the air chamber, a rotary valve being mounted in a region which provides a communication between the both chambers. An air pressure controlling rod is connected to the rotary valve. In a shock absorber of this type, the oil pressure controlling rod and the air pressure controlling rod are coupled to the rotary shaft of the single electric motor through a set of reduction gearings. Accordingly, there is a one-to-one correspondence between the angle of rotation of the oil pressure controlling rod and the angle of rotation of the air pressure controlling rod.
In a typical shock absorber of the prior art, the attenuation exerted is established at two levels, high and low, or at three levels of high, medium and low. Where the attenuation is established at two levels, the reduction gearing, for example, is provided with stops which permit the oil pressure controlling rod to rotate within a given angular range from a high to a low end or conversely from a low to a high end while preventing the rod to rotate beyond such angular extent. Representing a time period by T during which the motor is energized to rotate the oil pressure controlling rod through the permitted angular range or through a slightly extended range, the high level of attenuation can be established by energizing the motor for an interval T in the forward direction while the low level of attenuation can be established by energizing the motor for the same interval T in the reverse direction, thus dispensing with the switches or the potentiometer which is required in detecting the angular position. In addition, the hardware of the motor control circuit can be simplified. Where the motor drive is controlled by an electronic equipment such as a microprocessor, the control logic can be simplified. If the motor is energized for the interval T in a direction to exceed either limit position in response to a command which requires a high (or low) level of attenuation when the oil pressure controlling rod is at its high (or low) limit position, the motor will be energized without any rotational movement or will be overloaded since the reduction gearing is constrained by the stop, but any damage to the motor does not occur since the interval T is relatively short in duration. In other words, both the motor and the motor drive are constructed so as to be fully capable of withstanding the energization for the interval T without accompanying any rotation. It is also possible to design a control logic which prevents such energization without accompanying rotation from occurring in a motor control.
In a shock absorber which is designed to establish three levels, namely, high, medium and low, of attenuation, an arrangement is made such that a rotary plate, for example, is secured to the oil pressure controlling and rod and is formed with a single aperture which is located so as to correspond to the "medium level" of attenuation. The actuator also includes a solenoid assembly having a plunger which is located opposite to the aperture in the rotary plate whenever the oil pressure controlling rod assumes a position corresponding to the "medium level" of attenuation. When the oil pressure controlling rod is driven to the "medium" position where the solenoid is off and the plunger is urged by an associated spring to move into the aperture formed in the rotary plate from either position corresponding to the "high level" or "low level" of attenuation where the solenoid is off and the plunger is urged by a spring to abut against the surface of the rotary plate, the solenoid assembly is left deenergized while the motor is energized in either forward or reverse direction for substantially an interval of T/2. When the aperture in the rotary plate has rotated to a position directly below the plunger or when the oil pressure controlling rod has rotated to its "medium" position, the plunger is driven into the aperture in the rotary plate under the resilience of the spring. Conversely, when the oil pressure controlling rod is driven from a position corresponding to the "medium" level of attenuation to either position corresponding to the "high" or "low" level of attenuation, the solenoid assembly is energized to withdraw the plunger from the aperture in the rotary plate against the resilience of the spring, and the motor is energized in either reverse or forward direction for an interval substantially equal to T/2. The solenoid assembly is deenergized after the plunger has been withdrawn from the aperture.
Any of such shock absorbers which are designed to establish two or three levels of attenuation may be provided with a position sensor such as an angular position detecting switch assembly or a potentiometer. In such instance, the energization of the motor in forward or reverse direction or deenergization thereof is controlled on the basis of a status signal from the position sensor. The on/off control of the motor alone is insufficient to achieve an accurate positioning of the oil pressure controlling rod due to the inertia of the motor and its associated mechanism, but the combination of the stops which determine the "high" and the "low" level of attenuation, the rotary disc which determines the "medium" position and its associated solenoid assembly permits an accurate positioning to be achieved. In this manner, the energization of the motor without accompanying its rotation is substantially eliminated.
Referring back to the shock absorber which is designed to establish three levels of attenuation, the free end of the plunger of the solenoid assembly is urged against the rotary plate, which is used to establish a position corresponding to the "medium" level of attenuation, under the resilience of the coiled compression spring, as mentioned previously. The plunger must be advanced into the aperture smoothly when the rotary plate has rotated to place its aperture directly below the plunger. This requires that the aperture has a diameter which is greater than the diameter of the plunger. A difference between the diameters represents a play, which represents an error in determining the position corresponding to the "medium" level of attenuation. It will be seen that it is desired to provide as small a difference as possible between the diameters. However, a small difference in the diameters results in difficulty in causing the plunger to advance into the aperture, and any incomplete advancement of the plunger into the aperture results in a localized deformation or abration of the edge of the aperture and/or the free end of the plunger. Such deformation aggravates the advancement of the plunger into the aperture and also increases the degree of deformation to a greater degree. It is thus seen that the aperture in the rotary plate must be substantially oversized than the plunger, even though this results in an increased magnitude of error in the position which is achieved corresponding to the "medium" level of attenuation. Thus it will be seen that a mechanism for determining the position corresponding to the "medium" level of attenuation which comprises a combination of the rotary plate and the solenoid assembly involves a difficulty that the positioning accuracy and the positioning stability are two conflicting factors.